The invention is based on a method for ascertaining the content of an ingredient of flux in automatic soldering machines as defined hereinafter.
Electronic components are soldered onto printed circuit boards in automatic soldering machines; the surfaces to be soldered have to be moistened first with a flux. Fluxes of this kind comprise solid or active ingredients such as colophon, organic salts and acids, on the one hand, and a thinner in the form of organic solvents with a certain proportion of water, on the other. Only when the flux composition is constant can uniform soldering results be assured. This requires monitoring the content of the various ingredients of the flux used and correcting it as needed by adding thinner or by replacing the flux. A change in the content of the various ingredients occurs especially because, first, the volatile solvents evaporate during soldering, thereby increasing the concentration of solid or active ingredients in the flux, and second, the solvents used are highly hygroscopic, so that the water content increases with time.
In the laboratory, determining the content of the various ingredients of flux can be done without any particular difficulty; but with a soldering machine in operation, making such a determination so as to assure an always-constant flux composition is too time-consuming. Adjusting the constant flux composition therefore requires fast measurement during soldering machine operation. In known methods for determining the solid or active ingredient content in flux during the operation of an automatic soldering machine (German patent disclosure documents DE-OS 37 37 564 and DE-OS 35 37 368), photometric titration is performed for this purpose. In this process, some of the flux is withdrawn from the automatic soldering machine, and the transparency of the sample is measured as a function of the addition of a process fluid. These methods have the disadvantage, however, that the flux required for the measurement cannot be used as flux later because process fluid will have been added, and so it has to be disposed of as a waste product, and that the measuring instrument for measuring the added quantity of process fluid is complicated in structure and vulnerable to malfunction. For this reason, to assure good soldering results, it is often typically done to simply replace the flux in the automatic soldering machine completely and dispose of it at regular time intervals, such as once a week, without checking these ingredients.